Hazards thermal

Much information can be understood by a review of certain thermophysical properties of materials and mixtures. In comparing the values of heats of reaction, heats of decomposition and CART to values for known hazardous compounds, an estimation of thermal hazard potential can be made. Table A.2 outlines thermal hazard ranking values that could be used in classifying materials and processes based on heats of reaction and CART determinations (Melhem and Shanley 1997). 

Two standard estimation methods for heat of reaction and CART are Chetah 7.2 and NASA CET 89. Chetah Version 7.2 is a computer program capable of predicting both thermochemical properties and certain reactive chemical hazards of pure chemicals, mixtures or reactions. Available from ASTM, Chetah 7.2 uses Benson s method of group additivity to estimate ideal gas heat of formation and heat of decomposition. NASA CET 89 is a computer program that calculates the adiabatic decomposition temperature (maximum attainable temperature in a chemical system) and the equilibrium decomposition products formed at that temperature. It is capable of calculating CART values for any combination of materials, including reactants, products, solvents, etc. Melhem and Shanley (1997) describe the use of CART values in thermal hazard analysis. 

Experimental screening involves conducting experimental tests to gauge the thermal hazard of materials and processes. The goal of these tests is to provide information by which the materials and processes may be characterized. Experimental screening can be performed for the following ... 

Centrifuging of Test material for impact/shock sensitivity and unstable material, thermal hazards shock sensitive, alternate (low energy) separation process for material could shock sensitive/unstable material result in decomposition. CCPS G-13... 

Implement functionality testing Perform Thermal Hazards Analysis (THA)... 

Cronin, J. E. A Strategy for Thermal Hazards Analysis in Batch Chemical Manufacture, Thesis, Department of Chemical Engineering, South Bank Polytechnic, 1987. 

Gay, D. M., and D. J. Leggett (1993). Enhancing Thermal Hazard Analysis Awareness With Compatibility Charts. Journal of Testing and Evaluation 21, 6, 477-80. 

Chemical PPE In a fire or thermal energy hazard, PPE worn by responders should meet, at a minimum, the criteria in 29 CER 1910.156 (e), Eire Brigade Standard, requiring turnout gear. In conditions where skin absorption of a hazardous substance may result in substantial possibility of immediate death, serious illness, or injury or impaired ability to escape, totally encapsulated chemical protective suits should be used. It is vital to keep heat resistance of the totally encapsulated suits and the heat resistance of any PPE used underneath or in conjunction with the totally encapsulated suits in mind any time there is a thermal hazard. 

Hardee, H. C., and D. O. Lee. 1973. Thermal hazard from propane fireballs. Trans. Plan. Tech. 2 121-128. 

Williamson, B. R., andL. R. B. Mann. 1981. Thermal hazards from propane (LPG) fireballs. Combust. Sci. Tech. 25 141-145. 

In most cases, the BLEVE fireball is assumed to touch the ground (z = DJ2). For large scale BLEVEs, the assumption that the fireball is at its maximum diameter and rests on the ground will predict thermal hazard quite accurately. 

Thermal Hazards. These hazards include liot surfaces, fire produced by reacting substances, and flame contacts from heat-producing equipment, welding operations, and so on. 

Duswalt, A. A., Experimental Errors in Predicdons of Thermal Hazards, Ibid., p. 55. 

A small amount of hydrazine hydrate was present in the reaction mixture at this point, but a safety evaluation indicated the final reaction mixture had a very low thermal potential (AH = 15.3 J/g). This poses a minimum thermal hazard for vacuum distillation. 

Hydrazides (RCONHNH2) are highly useful starting materials and intermediates in the synthesis of heterocyclic molecules.2 They can be synthesized by hydrazinolysis of amides, esters and thioesters.3 The reaction of hydrazine with acyl chlorides or anhydrides is also well known,4 but it is complicated by the formation of 1,2-diacylhydrazines, and often requires the use of anhydrous hydrazine which presents a high thermal hazard. Diacylation products predominate when hydrazine reacts with low molecular weight aliphatic acyl chlorides, which makes the reaction impractical for preparatory purposes.5... 

For perspective, 1 g of hydrazine monohydrate is equivalent to (TNT) in terms of thermal potential T. Grewer, Thermal Hazards of Chemical Reactions Elsevier Amsterdam, 1994, Vol. 4. 

Figure 5.4-57. Programmable DTA plot.s for variou.s heating rates 4-nitrobenzoic acid (reprinted from Grewer (1994), Thermal hazards of chemical reactions , Copyright (1994) with permission from Elsevier Science). 

Grewer, Th., 1994, Thermal Hazards of Chemical Reactions , Elsevier, Amsterdam. 

Solutions of the hydroperoxide in halogenated solvents, and especially dichloro-ethane are much less stable than in toluene (reference 5 above). On a large scale, the azeotropic drying of solutions of the hydroperoxide in dichloroethane may present a thermal hazard. 

Purser, D.A. "Toxicity Assessment of Combustion Products and Modeling of Toxic and Thermal Hazards in Fire," SFPE Handbook of Fire Protection Engineering, National Fire Protection Association, Quincy, MA, Section 1, 1988, pp. 200-245. 

D. I. Townsend and J. C. Tou, Thermal Hazard Evaluation by an Accelerating Rate Calorimeter, Thermochimica Acta (1980), 37 1-30. 

The potential thermal hazards associated with thermally unstable substances, mixtures, or reaction masses are identified and evaluated as in the flow charts Figures 2.3, 2.4, and 2.5. The potential hazards posed by reactivity—water reactivity, pyrophoricity, flammability, oxidizer contact, and so forth—are also included in Figure 2.3. The individual boxes in the flow charts are discussed below ... 

The screening tests can be run in the absence or presence of air to differentiate the thermal hazards due to decomposition of the substance from those due to reactivity of the substance with oxygen. 

If the substance does not meet any of the four mentioned criteria, the substance may be recognized as having a low risk to handle from the point of view of thermal hazards. 

The investigation of thermal hazards of materials containing an inhibitor, or... 

Most of the DSC equipment can be used in the temperature range of 25°C to 500°C. Most can be cooled as well, a feature required for investigating samples that are unstable at ambient conditions. DSC equipment is usually sufficient for indicating thermal hazards of stirred systems and small-scale unstirred systems provided the reaction is kinetically controlled under normal operating conditions, but the resulting data must be used with careful judgment if mixing or mass transport are important. 

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